Mapping a black hole’s magnetic field, using a pulsar

Supermassive black holes at the centers of galaxies generate a lot of light, produced by hot plasma swirling around them. That plasma both produces and is shaped by powerful magnetic fields — at least according to theory. In the case of the Milky Way, new observations have provided the first measurements of the magnetic field surrounding the black hole, thanks to the presence of a newly-discovered pulsar. My latest article for Ars Technica has the story:

Astronomers hoped fondly for the discovery of a pulsar, a rapidly rotating remnant of a dead star, which generates powerful jets of radio photons. Any magnetic field near the pulsar would affect the radio emissions, allowing researchers to map the environment near the black hole.

The wish was granted earlier this year when an X-ray flare revealed the presence of a pulsar within one light-year of the Milky Way’s black hole. R.P. Eatough and colleagues measured the light from the pulsar and found it was strongly rotated, a sure sign of a magnetic field. The magnetic field they detected—if it extends to the surface of the black hole—would be sufficient to explain the entire spectrum of emissions from the Milky Way’s center. [Read more….]